Allow reconstruct of UUID via UUID#fromNative

I think it's better to allow UUID#fromNative like Rhumsaa\Uuid\Uuid#fromString do. Otherwise it's hard to reconstruct the UUID from persisted state, like you would do in a [doctrine mapping type](http://doctrine-orm.readthedocs.org/en/latest/cookbook/custom-mapping-types.html). With current solution you need reflection or a decorator to apply persisted UUID string.